As a method of treating organic effluent such as sewage and food factory effluent, there have been known an active sludge method, a biofilm method and a stabilization pond method or the like. However, since excess sludge is generated in large quantity in a treating apparatus in these methods, sludge treating apparatuses such as a dehydrator, a drier and an incinerator are required. Since high phosphor concentration in effluent causes problems such as eutrophication in a closed water area, the concentration of phosphor in the effluent is regulated with those of COD and nitrogen.
In recent years, many organic effluent treatment methods generating little excess sludge have been proposed, and examples thereof include a bacteriolysis-potential increasing method, a maintenance metabolizing method, an uncoupling metabolizing method, a maintenance metabolizing method, and a bacteria preying method (Non-Patent Document 1). The bacteriolysis-potential increasing method dissolves sludge to promote latent multiplication, and examples for dissolving sludge include a chlorine method, a bead mill method, a high revolution disk method, a supersonic method, a hydrothermal method, and a chemical agent adding method in addition to an ozone method described in Patent Document 1 (JP-A-07-116685), a thermophile method described in Patent Document 2 (JP-A-11-235598). Examples of the maintenance metabolizing methods include a membrane bioreactor method described in Patent Document 3 (JP-A-2005-46748). Examples of the uncoupling metabolizing methods include a method using a chemistry uncoupling agent. Examples of the bacteria preying methods include a two-step system.
The above organic effluent treatment methods have an advantage and a disadvantage respectively. However, the methods have a problem that the phosphor concentration in treatment water is increased as compared with the case where excess sludge is generated in large quantity.
Therefore, there has been required a method of treating organic effluent capable of generating excess sludge in small quantity and efficiently reducing the phosphor concentration in the treatment water.
On the other hand, there has been known a method of reducing and removing ions contained in effluent by a precipitaion-sedimentaion treatment or an ion adsorption treatment as a method of treating inorganic effluent which hardly contains organic ingredients such as COD of effluent in a ceramic industry factory. The precipitaion-sedimentaion treatment can treat effluent containing ions to be removed in a comparatively high concentration. However, a chemical agent needs to be added in large quantity in aiming a so-called advanced treatment where the concentration of the ions to be removed in the treatment water is set to 1 mg/L or less, and unfortunately, the sludge is also generated in large quantity.
On the other hand, although the ion adsorption treatment is excellent in the advanced treatment of effluent, an adsorbent is required in large quantity in adsorbing the effluent containing ions to be removed in a high concentration, and the regeneration frequency of the adsorbent is also increased. Accordingly, unfortunately, the chemical agent for the regeneration of the adsorbent is also required in large quantity to increase operating cost.
Then, there has been considered a method of combining the precipitaion-sedimentaion treatment and the ion adsorption treatment in series to treat effluent as a method of solving the problem of each of the precipitaion-sedimentaion treatment and ion adsorption treatment (JP-A-10-314798 (Patent Document 4) and JP-A-2001-276814 (Patent Document 5)). This method roughly removes ions to be removed, the ions contained in the effluent in the precipitaion-sedimentaion treatment, and supplies precipitaion-sedimentaion treatment water in which the ions to be removed are removed to some extent to the subsequent ion adsorption treatment. Since the adsorbent used in the ion adsorption treatment is saturated by the adsorption of a fixed amount, a regeneration treatment is performed using a regenerated solution even in this case. This regeneration treatment produces reproduced drainage containing the ions to be removed, the ions desorbed from the adsorbent. However, the treatment returns the drainage to the precipitaion-sedimentaion treatment to retreat the drainage.
However, there has been required a method of more efficiently providing treatment water containing the ions to be removed in low concentration for inorganic effluent.
Also, there have been known treatments using a reverse osmosis membrane apparatus, an electric deionization apparatus, a distillation apparatus and an ion exchange apparatus using an ion exchange resin or the like as a treating method of providing water having high purity from the inorganic effluent.
However, the case where ions of a certain type cannot be removed to a desired level often occurs from the relationship or the like between the characteristic of each of the treating methods and the concentration of ions contained in raw water provided for the treatment.
For example, treatment water (freshwater) prepared by treating sea water using a reverse osmosis membrane apparatus has water quality mostly satisfying a WHO quality guideline value. However, it is difficult to set only boron to a WHO recommendation value (0.5 ppm) or less.
Therefore, JP-A-10-85743 (Patent Document 6) has proposed a method of treating sea water concurrently using a reverse osmosis membrane apparatus and an ion exchange apparatus using a boron selective ion exchange resin to set the boron concentration to a WHO recommendation value or less.
However, since the boron adsorbing capacity of the boron selective ion exchange resin is not so large, the boron selective ion exchange resin has economical problems such as the increase in the scale of the ion exchange apparatus and the increase in the regeneration frequency and exchange frequency of the ion exchange resin.
Even when the electric deionization apparatus treats tap water to produce ultrapure water, the water quality of ultrapure water may be insufficiently obtained without sufficiently removing boron depending on the type of raw water. Even in this case, water treated by the electric deionization apparatus is post-treated using the ion exchange apparatus using the boron selective ion exchange resin (JP-A-8-89956 (Patent Document 7)). However, the treatment has economical problems such as the increase in the scale of the ion exchange apparatus and the increase in the regeneration frequency and exchange frequency of the ion exchange resin.
As described above, there is need for an apparatus and method capable of efficiently reducing and removing ions contained in water to a low concentration in various water treatment fields.    Patent Document 1: JP-A-07-116685    Patent Document 2: JP-A-11-235598    Patent Document 3: JP-A-2005-46748    Patent Document 4: JP-A-10-314798    Patent Document 5: JP-A-2001-276814    Patent Document 6: JP-A-10-85743    Patent Document 7: JP-A-08-89956    Non-Patent Document 1: Y. Wei et al., “Minimization of excess sludge production for biological wastewater treatment”, Water Research, 37 (18), 4453-4467 (2003)